Completed Tasks filter?

I can't figure out why the Completed tasks filter only works sometimes. If I have a Saved Search which does not filter out completed tasks, I should be able to filter them out by turning off the "Completed Tasks" in the filter criteria, but it doesn't work? Anyone know why?

This would be very hand for me in some Searches, to be able to turn on and off the Completed Tasks filter without having to redo the Search.

I was not able to reproduce this. I pulled up a search of mine that showed completed tasks. Then I unchecked the filter and they disappeared. Can you please create a support ticket and let us know the details about your search criteria?